Remote Sensing of Thermal Water Stress Indicators in Peach

Canopy temperature is a well known indicator of water stress, as any reduction in canopy conductance due to stomatal closure results in a further increase of canopy temperature. However, canopy temperature is affected by different ambient factors, such as air temperature, vapor pressure deficit, and net radiation, among others. Standardization is required in order to obtain reliable indicators of plant water status from canopy temperature. Different approaches have been developed during the past decades, such as the Crop Water Stress Index (CWSI) developed in the 80s by Idso and Jackson's group (Idso et al., 1981), providing a normalized 0-1 index to quantify water stress independently of air temperature and humidity. Nevertheless, extensive use of thermal based indicators to map water stress has been limited by the lack of spatial and temporal resolution of satellite sensors. Airborne thermal scanners could provide an alternative, but the high operational costs and complexity have limited their use to real applications. Nowadays the use of commercial off-the-shelf thermal sensors onboard of Unmanned Aerial Vehicles (UAVs) offers a new important monitoring option for water management of high value crops such as fruit trees.